A. Field of the Invention
The present invention relates generally to an apparatus for testing composite materials, and, more particularly to a dynamic interphase-loading apparatus for testing composite materials and a method of using the same.
B. Description of the Related Art
Recent studies of composite materials show that the properties of the resin at the fiber/matrix interface region are different than those of the bulk resin. The fiber/matrix region forms during processing of the resin and is known as the interphase. Fiber/matrix interphase properties play an important role on the performance of the composite. Modification of the interphase could change the modes of failure and energy-absorption characteristics. Therefore, significant efforts have been directed at developing a fundamental understanding of the role of interphase. In order to properly understand interphase, one must first be able to accurately test the mechanical properties of the interphase.
Several macromechanical testing techniques have been developed to test the ballistic and impact properties of the composites under dynamic loading conditions (i.e., under high strain rates), as well as quasi-static loading conditions. As shown in FIG. 1(a), such dynamic macromechanical testing techniques include the Hopkinson bar, gas gun, plate impact, and weight drop techniques. As shown in FIG. 1(b), macromechanical test techniques, such as short beam shear and flexural bending, have been used to characterize interphase under quasi-static conditions. However, these techniques fail to directly obtain interphase-related data or to isolate the effects of interphase because mechanical loading applied to the composite induces complex stress states within the fiber/matrix interphase that are not well defined. Thus, these techniques provide useful but qualitative information about interphase.
Micromechanical testing techniques that can directly characterize the interphase properties have been developed, but are limited to testing interphase properties under quasi-static loading conditions. As shown in FIG. 1(c), such micromechanical techniques include the single fiber fragmentation, fiber pull-out, and microindentation techniques.
Thus, there is a need for a new micromechanical test technique that can directly characterize the interphase properties under dynamic (high-strain rate) loading conditions.
An object of the invention is to provide a micromechanical testing technique that obtains interphase-related data under quasi-static and dynamic (high-strain rate and fatigue) loading conditions.
Another object of the invention is to provide an apparatus that permits directly testing of the interfacial shear strength, energy absorbing capability, shear stress (xcfx84)-shear strain (xcex4) behavior and elastic modulus and durability (fatigue life, residual strength after fatigue loading or exposure to a hot, wet environment) of various-sized fiber/matrix systems under quasi-static and dynamic (high strain rate) loading conditions.
A still further object of the invention is provide a testing apparatus and method that overcomes the problems associated with the related art.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a dynamic interphase-loading apparatus (DILA) for testing the mechanical properties of an interphase region of a fiber/matrix composite under quasistatic to dynamic loading conditions, the apparatus comprising: means for providing a quasi-static to dynamic load to the fiber/matrix interphase; means for continuously monitoring the load applied to the fiber/matrix composite and providing a signal representative thereof; means for continuously monitoring the displacement of the interphase of the fiber/matrix composite and providing a signal representative thereof; means for forming various inputs signal to activate the piezoelectric actuator and to generate various displacement rates; and a computing means for receiving the load signal from the load monitoring means, for receiving the displacement signal from the displacement monitoring means, and for providing an input signal to the piezoelectric actuator, the computing means having a memory means connected to a processing means, wherein the processing means stores the load signal in the memory means, generates the input signal supplied to the piezoelectric actuator, and generates information representing the mechanical properties of the interphase of the fiber/matrix composite.
To further achieve the objects, the present invention comprises a method for testing the mechanical properties of an interphase region of a fiber/matrix composite under quasi-static to dynamic loading conditions, the method comprising the steps of: using a diamond tip as a probe to load the interphase; providing a quasi-static to dynamic load to the fiber/matrix interphase; debonding the fiber from the matrix at the interphase region and eventually pushing the fiber out from matrix; continuously monitoring the load applied to the fiber/matrix composite and providing a signal representative thereof; continuously monitoring the displacement of the interphase of the fiber/matrix composite and providing a signal representative thereof; receiving the load signal and the displacement signals in a computing means having a memory means connected to a processing means; providing a control signal to the piezoelectric actuator, via the computing means; and using the processing means of the computing means to store the load signal in the memory means, generate the control signal supplied to the piezoelectric actuator, and generate information representing the mechanical properties of the interphase of the fiber/matrix composite.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.